Public swimming ups risk of gastrointestinal ills

NEW YORK (Reuters Health) - A dip in the public pool or local lake may boost people's odds of catching a case of "stomach flu," a new study shows.

Australian researchers found that among more than 2,800 adults and children they followed for 15 months, participants were somewhat more likely to develop gastroenteritis in the week or two after a public swim.

Gastroenteritis refers to inflammation in the gastrointestinal tract caused by viral, bacterial or parasitic infection. The symptoms -- what people commonly identify as "stomach flu" -- include abdominal pain, vomiting, diarrhea and fever.

Contaminated food and drinking water are common sources of infection, and recreational swimming has been linked to outbreaks of gastrointestinal illness. But the extent to which swimming, in different types of venues, raises the odds of gastroenteritis has been less clear.

In the current study, participants' gastroenteritis risk was about one-quarter higher in the one to two weeks after a visit to a public pool or spa, versus other weeks. The odds went up 77 percent, on average, in the week after a swim in a river or lake, while a similar increase was seen among adults who had taken an ocean dip in the past two weeks.

The findings, the researchers write in the American Journal of Epidemiology, confirm that swimming in fresh, salt or treated waters can pose a risk of gastroenteritis.

Still, the investigators are not advising people to retire their swimming trunks.

The increases in gastroenteritis risk were "relatively small," and swimming, as a form of aerobic exercise, can also have health benefits, note Katie Dale and colleagues at Monash University in Melbourne.

There is, however, a need for better preventive measures, the researchers write.

In Melbourne, they note, health authorities recommend that to prevent disease transmission, people with diarrheal illnesses not get into a public pool for at least one week after their symptoms have cleared.

That window extends to two weeks for people with confirmed cases of giardiasis or cryptosporidiosis -- two parasitic waterborne infections.

However, no one knows how well people follow that advice. In addition, Dale's team notes, there are no specific guidelines regarding swimming in lakes, rivers or oceans.

The findings are based on information gathered from 600 Melbourne families over 15 months; the families used weekly diaries to record any swimming activities, illnesses, medication use and travel.

Over the study period, there were nearly 2,700 cases of probable gastroenteritis, affecting half of the study participants.

In general, the odds of contracting gastroenteritis were higher in the week or two following a swimming outing for both adults and children. And risks were seen with all types of venues.

The findings, according to Dale's team, point to the need for prevention efforts in all types of swimming settings.